This section provides background information relating to the present disclosure which is not necessarily prior art.
Transfer cases are used in particular in motor vehicles with all-wheel drive. They serve to distribute a torque generated by the engine and made available to an input shaft of the transfer case to at least two output shafts of the transfer case, each drive-connected to motor vehicle axles. Along the power flow from the engine of the motor vehicle to the power axle of the motor vehicle the transfer case is usually arranged on the output side of the main gearbox of the engine, which serves to transmit the torque generated by the engine.
A basic distinction is made, according to the type of transfer case, between differential-controlled transfer cases and clutch-controlled transfer cases. In the case of differential-controlled transfer cases either a manually or an automatically lockable differential and/or planetary gear distributes the power flow to two output shafts permanently coupled to the input shaft. In the case of clutch-controlled transfer cases the power flow is distributed to two output shafts by an automatically and/or manually actuated clutch, generally a multi-disk clutch. Here one output shaft of the transfer case, the so-called primary shaft, has a permanently operative drive coupling to the input shaft, and a further output shaft, the so-called secondary shaft, has a drive coupling to the input shaft selectively actuated via the clutch, as and when required. Clutch-controlled transfer cases are also termed “disconnect” transfer cases, since these allow one of the two output shafts of the transfer case to be coupled to/decoupled from the drive shaft.
In addition, hybrid forms are equally known, which comprise both a differential and/or a planetary gear, together with one or more clutches. In such transfer cases the drive torque introduced by way of an input shaft is similarly distributed via the differential and/or planetary gear between at least two output shafts, so that the two output shafts are permanently driven, but a relative rotation is nevertheless allowed between the two output shafts. The clutch here serves for selectively locking the one output shaft to the other output shaft, so that both shafts are forcibly driven.
Transfer cases often comprise an offset mechanism, thereby either giving the output shafts an axial offset in relation to one another and/or giving one or both output shafts an axial offset in relation to an input shaft that is or can be connected to the engine of a motor vehicle. Toothed wheels and/or flexible traction drives are preferably used as offset mechanism.
Flexible traction drives comprise a traction element, which transmits propulsive power between the shafts having an axial offset. Flexible traction drives are preferably used in the form of chain or toothed-belt drives, in which the propulsive power is transmitted via a driving traction element pulley in the form of a toothed wheel, for example, to the traction element, for example a chain or a belt, to a driven traction element pulley, the driving traction element pulley being arranged, for example, on the input shaft and the driven traction element pulley on an axially offset output shaft of a transfer case, for example.
The traction element is typically tensioned between the two traction element pulleys, so that no slip occurs between the two shafts. Acting on the shafts here is a traction element tensile force, which in current transfer cases is transmitted from the driving traction element pulley via various bearings and shafts into the housing of the transfer case and back to the driven traction element pulley again. All the components involved here are exposed to high stress loads. These stress loads must always be taken into account when designing the components and often lead to a greater component outlay and therefore also to an increased cost outlay.